He's constantly scratching to the point of causing patches of baldness and chewing his fur to where he's ingesting it and its visible in his stool. He's 5 months old and aggressive and likes to chew on everything. My dog is a cockapoo

And your vet says??

One of several guesses is a too dry winter house.
Please google 'winter dry air dog skin' or something like that.
Walk your dog more, don't shampoo in winter except for this time, try some oatmeal/aloe soothing baths, no hair dryers.

But there are other conditions such as mange, so since it's so bad, see a vet.

Also spend more time with your dog. Puppies need training, and it all takes time. No puppy should be chewing on 'everything.' He gets dog toys and is patiently taught (praised)which ones are OK to play with.
If you work a lot, hire someone to come in during mid-day, and also to walk him.

There are too many possibilities for us to guess.

This could be an allergy, as many dogs have them. Sadly, if it is an allergy you have a long road ahead of you trying to figure out what is causing the allergic reaction.

It could be a skin condition.

It could be a nerological condition.

It could be many other things, too many to list them all.

Time to see your vet.